Medical personnel have to exercise the utmost of care when using conventional syringes so as not to be accidentally punctured by a contaminated syringe needle resulting in possible exposure to infectious diseases, such as acquired immune deficiency syndrome (AIDS) or serum hepatitis when injecting a medicament into a patient.
While various safeguards have been provided, such as protective caps for covering a used needle and sharps containers for the disposal of the used needle, it has been found that the chance of accidental puncture is most likely to occur during the manipulation of the syringe to either cap the needle or inverting the used needle into the sharps container.
In an effort to improve the safeguards for used syringe needles, it has been proposed to provide the syringe with a sleeve slidably mounted on the syringe barrel and movable from a retracted position on the syringe barrel to an extended position at the distal end of the barrel, to thereby provide a shield surrounding the used needle. The sleeve is releasably held in the retracted and extended positions by detents which are manually actuated by the user. These sleeve-type shields have not proven entirely satisfactory due, mainly, to the manual dexterity required by the user to release one detent for sliding the sleeve to the needle protecting position and then to actuate another detent for holding the sleeve in the extended position.
In order to overcome the disadvantages experienced in hitherto employed shielded medical syringes, the disposable shielded medical syringe of the present invention has been devised which comprises, essentially, a syringe barrel including a plunger threadably connected to a piston on the end thereof, the piston being slidably mounted in the barrel in sealing engagement with the barrel side wall. The syringe needle is connected to a second piston assembly slidably mounted with the barrel, in sealing engagement with the barrel side wall and located between the distal end of the barrel and the plunger piston. The plunger piston is adapted to be threadably connected to the needle piston assembly for withdrawing the contaminated needle into the syringe barrel. By this construction and arrangement, medicament is dispensed from the syringe by pushing the plunger toward the distal end of the barrel. After the medicament has been dispensed, the plunger is rotated to threadably couple the plunger piston to the needle piston assembly. The plunger is then pulled toward the proximate end of the barrel, thereby causing the contaminated needle and associated piston assembly to be withdrawn to a shielded position within the syringe barrel. The plunger is then disconnected from its piston and discarded, to thereby prevent the needle and associated piston assembly from being pushed once again toward the distal end of the barrel.
To complete the shielding of the used needle, a cap or scabbard is inserted into the distal end of the syringe barrel.
A spring clip is mounted on the proximate end portion of the syringe barrel providing a stop member to prevent the syringe plunger from being pulled completely out of the barrel.